The central processing unit (CPU) is an integrated circuit (IC), and is one of many integrated circuits included in electronic devices, such as modern computers (not shown). CPUs may perform operations on data and transmit the results to other integrated circuits. Therefore, the CPU's function is vital to the overall performance of a computer. The structure that surrounds the CPU within the computer also plays a key role in aiding and protecting the CPU in a computer.
FIG. 1 shows an integrated circuit housing, which includes typical components that surround the CPU in a computer or other electronic device. In the center of the figure, an IC, i.e., a chip (6), operates on top of a ceramic land grid array (CLGA) package (8). The CLGA package (8) contains small shaped metal pads (not shown) that connect to internal wires leading up to the chip (6). A socket (10) is an electrical interconnect that locates both the chip (6) and the CLGA package (8). The socket (10) allows the chip (6) to electrically interface with a printed circuit board (PCB) substrate (12) through the CLGA package (8). The PCB substrate (12) also contains metal pads (not shown) on the surface that correspond to the metal pads on the CLGA package (8) beneath the chip (6). Each individual connection that is made between the PCB substrate (12) and the CLGA package (8) components is called a contact (14). All of the aforementioned internal components surrounding the chip (6) may be collectively referred to as a stack.
Continuing with FIG. 1, the stack is typically surrounded by clamping hardware. Typical clamping hardware may include a heat dissipater (2) (e.g., a heat sink), a bolster plate (18), and typically as many as four fasteners (4). The heat dissipater (2) may be affixed to the bolster plate (18) via four fasteners (4) that fasten through the PCB substrate (one on each corner of the bolster plate). The bolster plate (18) is typically a rigid and stiff element. In between the bolster plate (18) and the backside of the PCB (12) is a thin insulator (16) made of plastic type material, which is typically included for its electrical properties.
When the fasteners (4) are tightened, the clamping hardware imparts a load on the contacts (14) between the chip (6) and the PCB substrate (12). Due to the large number of contacts per circuit board and the force required for electrical function of each contact (14), the load applied by the clamping hardware may be quite large. For example, a typical 37 by 37 PCB substrate (12) includes approximately 1,368 contacts. The finite stiffness of the clamping hardware does not allow for the load to be spread across all the contacts (14) and causes a non-uniform load that is concentrated on the four corners where the fasteners (4) are located.
The uniformity of load distribution applied to the contacts (14) is important for the electrical function of each individual contact (14). In an effort to improve load distribution, some conventional devices use a spherical or cylindrical curvature within the clamping hardware to redistribute the load. For example, a curvature may be placed in the center of the bolster plate. This allows a portion of the load to be offset from the four corners to the center of the clamping hardware. Alternatively, a flat, extremely stiff bolster plate may be used to spread the load away from the four corners.